Explain the mechanism of the C 4 cycle.

The C 4 pathway acts as a mechanism to build up high concentrations of carbon dioxide in the chloroplasts of the bundle sheath cells. The mechanism takes place as follows: The C 4 pathway initiates with a molecule called phosphoenolpyruvate (PEP) which is a 3-carbon molecule. This is the primary CO 2 acceptor and the carboxylation takes place with the help of an enzyme called PEP carboxylase. They yield a 4-C molecule called oxaloacetic acid (OAA). This is converted into another 4-carbon compound known as malic acid. Later, they are transferred from mesophyll cells to bundle sheath cells. Here, OAA is broken down to yield carbon dioxide and a 3-C molecule. The CO 2 thus formed is utilised in the Calvin cycle whereas the 3-C molecule is transferred back to mesophyll cells for regeneration of PEP.

Explain cyclic photophosphorylation reaction.

The synthesis of ATP from ADP by using light energy in the chloroplast is called photophosphorylation. It is of two types: i) Cyclic Photophosphorylation and ii) Non-Cyclic Photophosphorylation. In cyclic photophosphorylation, only photosystem I (pigment group) takes part. The reaction centre of photosystem I absorb light of wavelength up to 700nm, hence, it is called P 700 . Electron released from P 700 by light energy in PS I passes through different electron acceptors like A (FeS), Fd - Cyt b- Cyt f through plastocyanin reaches back to P 700 . Energy release between Cyt b6 and Cyt-f, used in the synthesis of ATP from ADP. In this reaction, free electrons from P 700 , return back to the same, after synthesis of ATP. Thus, it is known as cyclic photophosphorylation.

What is photophosphorylation.

Photophosphorylation is the process of producing ATP from ADP molecules in the presence of sunlight. It is light dependent reaction and occurs in the thylakoid membrane of the chloroplasts. In this reaction accumulation of protons occurs in the lumen of chloroplasts. Light energy is used to create an electron donor and an electron acceptor. The electrons move from donor to acceptor by electron transport chain. It is of two types: i) Cyclic Photophosphorylation and ii) Non-Cyclic Photophosphorylation.

Explain the mechanism of the C 4 cycle.

The C 4 pathway acts as a mechanism to build up high concentrations of carbon dioxide in the chloroplasts of the bundle sheath cells. The mechanism takes place as follows: The C 4 pathway initiates with a molecule called phosphoenolpyruvate (PEP) which is a 3-carbon molecule. This is the primary CO 2 acceptor and the carboxylation takes place with the help of an enzyme called PEP carboxylase. They yield a 4-C molecule called oxaloacetic acid (OAA). This is converted into another 4-carbon compound known as malic acid. Later, they are transferred from mesophyll cells to bundle sheath cells. Here, OAA is broken down to yield carbon dioxide and a 3-C molecule. The CO 2 thus formed is utilised in the Calvin cycle whereas the 3-C molecule is transferred back to mesophyll cells for regeneration of PEP.